Calluses and corns are caused by repeated pressure or friction on an area of skin. The pressure causes the skin to die and form a hard, protective surface. A soft corn is formed in the same way, except that when sweat is trapped where the corn develops, the hard core softens. This typically occurs between toes.

What are calluses made of?

Biologically, calluses are formed by the accumulation of terminally differentiated keratinocytes in the outermost layer of skin.

Are calluses good?

Researchers found that calluses offer the foot protection while you're walking around, without compromising tactile sensitivity -- or the ability to feel the ground. That's in contrast to cushioned shoes, which provide a thick layer of protection, but do interfere with the sense of connection to the ground.